The evolution of efforts to achieve finer dimensions for elements of microcircuit devices while also making such devices larger has led to a variety of expedients involving both step and repeat and scanning processes. U.S. Pat. No. 5,281,996, for example, suggests exposure on a substrate of juxtaposed images of microcircuit patterns so that a lens having an image field smaller than the total pattern to be imaged can complete the imaging in two or more steps. This patent also suggests scanning an image with a long and narrow bar of actinic radiation spanning the image field.
U.S. Pat. No. 4,924,257 suggests raster scanning a full substrate with image patterns exposed within the shape of a regular hexagon sweeping repeatedly across the substrate in an overlapping pattern that exposes the substrate uniformly. Either a large pattern filling the whole substrate or a series of smaller patterns fitting within the hexagonal shape can be scanned this way. U.S. Pat. Nos. 5,285,236 and 5,291,240 offer similar suggestions.